🎵 Music
MP3/AAC/FLAC/WAV from SD, artist/album/playlist browser, ID3 tags (cached), shuffle & repeat, sleep timer, resume after reboot.
Fennek turns the LilyGO T-Deck Pro (ESP32-S3, E-Ink, LoRa) into a real handheld: listen to music, resume audiobooks, read eBooks and chat over the LoRa mesh via MeshCore — with a homescreen launcher, touch + physical keyboard, and background audio that keeps playing across app switches.
It is a standalone alternative to the factory firmware — built around the hardware's defining quirk, that E-Ink, the SD card and LoRa all share one SPI bus, while still delivering stutter-free audio playback.
Apps
🎧 Audiobook
Books as folders under /audiobooks, chapters natural-sorted, per-book bookmark, ±30 s jumps, sleep timer.
📖 Reading
.txt and .epub from /books, on-device EPUB conversion, page-index cache, per-book reading position.
📡 Mesh
Lean MeshCore client: public & hashtag channels, DMs with delivery status, contacts from adverts, message log on SD with history reload.
🎮 Games
2048, Minesweeper, Chess (Negamax AI) and Tic-Tac-Toe — game logic host-tested.
📝 Notes
One note per day under /notes. "+ Today" opens or appends; list shows every day newest-first with a preview.
🎙️ Podcast
Subscribe to RSS feeds (/podcasts/feeds.txt), sync the latest episode over Wi-Fi and keep only that one — downloaded straight to SD.
⚙️ Options
Radio presets (EU Narrow), individual LoRa parameters, node name, battery info, firmware version.
＋ More
Status line (battery, playback), key-lock & standby via the button, and a serial debug console over USB.
On the device
Rendered pixel-accurately from the real drawing code (240×320 E-Ink).
Engineering around the hardware
The T-Deck Pro is a lovely device with four awkward constraints. Fennek is really the story of working with them rather than against them — the defining one being that E-Ink, the SD card and LoRa share one SPI bus. The architecture revolves around audio never stuttering despite that, and inputs responding instantly:
- A dedicated audio-decode task on core 0, with a 256 KB PSRAM read-ahead.
- Every SPI access (SD, E-Ink, LoRa) serialized behind one mutex.
- The SPI bus is released during the E-Ink BUSY phase so the I2S DMA never runs dry.
- E-Ink refreshes only on real change; progress shown as a narrow region strip.
🕐 No real-time clock
There is no battery-backed RTC. The canonical clock is the ESP32 system
time, which survives deep sleep (the older millis() clock lost
the whole sleep duration). It is set, in priority order, from GPS,
NTP (when Wi-Fi is briefly up) and mesh adverts;
drift is learned over time and a future-dated packet can never drag the
clock forward unchecked.
🔋 Can't stay online
Staying connected forever isn't possible on this power budget — and Wi-Fi and audio can't even run at once (the Wi-Fi task on core 0 evicts the audio task). So Fennek never holds a connection: scrobbles, note polishing and podcast downloads are batched into a short Wi-Fi window before standby, and unused peripherals (GPS, haptics) are powered down at boot.
🧩 Only two cores
Two CPU cores mean barely any true multitasking. Fennek pins audio decoding to core 0 and the UI + mesh pump to core 1, pauses SD library scans while audio is playing, and runs heavier work (the chess AI) at low priority — so playback stays smooth and the keyboard stays responsive.
🖋️ E-Ink screen
E-Ink is gorgeous but slow, and full refreshes flash the whole panel. Fennek redraws only on a real change, paints progress bars and status as narrow region strips instead of full repaints, and stretches the anti-ghosting full refresh out to keep the screen calm.
The full set of anti-stutter invariants and
these design decisions live in
CLAUDE.md.
Hardware
LilyGO T-Deck Pro V1.1:
- ESP32-S3 — 16 MB flash, 8 MB PSRAM
- E-Ink GDEQ031T10, 240×320
- CST328 touch (I2C), TCA8418 keyboard
- PCM5102A DAC (I2S, 3.5 mm jack)
- SX1262 LoRa, BQ27220 fuel gauge, microSD
Build & flash
Prerequisite: PlatformIO. Connect via USB-C, then:
pio run -e fennek # build
pio run -e fennek -t upload # flash (USB-C)
pio device monitor -b 115200 # log + debug consoleRuns even without an SD card. Custom firmware replaces the factory software — flash at your own risk.